A honeycomb structure having a hexagonal cross-sectional shape is disclosed in Japanese Patent Laid-Open No. Hei 9-105013.
The honeycomb structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013 has a structure in which a surface formed by connecting end edges of ribs arranged in a honeycomb shape is a curved surface, and it has been attempted to apply the honeycomb structure to a shock absorbing member for helmets.
In manufacturing this honeycomb structure, as shown in FIGS. 20 and 21 of the drawings, a band-like blank material 01 that is directed rectilinearly in one direction and has a rectangular cross-sectional shape is fed between a pair of truncated conical rolls 02, and is rolled to have an elongate trapezoidal cross-sectional shape as shown in FIG. 21. Thus, a band-like blank material 01A is obtained in which the band-like blank material 01 directed rectilinearly in one direction is spirally wound.
The band-like blank material 01A that is spirally wound is divided into a plurality of portions, for example, three portions evenly over the winding direction, as shown in FIG. 23. The surface of the arcuate band-like blank material 01B is divided at regular angular intervals from the spiral center O into sections (X1, X2, X3, X2) (X1, X2, X3, X2) . . . , as shown in FIG. 22. In the surface of one of the adjacent arcuate band-like blank materials 01B, an adhesive is applied to the sections X1 intermediated by the three sections X2, X3, X2. In the surface of the other of the adjacent arcuate band-like blank materials 01A, an adhesive is applied to the central section X3 located at an intermediate position between the adhesive-coated sections X1. After curing of the adhesives, both upper and lower end portions of the band-like blank materials 01B that are divided into arcuate forms are broadened from each other as shown in FIG. 24, whereby a honeycomb structure as shown in FIG. 14 can be manufactured.
In order to manufacture the honeycomb structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013, a process is used in which the rectangular band-like blank material 01 having a cross-sectional shape with a fixed thickness over the longitudinal direction is formed into the band-like blank material 01A having an elongate trapezoidal cross-sectional shape. It is necessary to prepare a band-like blank material 01 which is free of dispersions in the width direction and in the thickness over the longitudinal direction thereof. At the same time, it is necessary that the accuracy of the outer peripheral surfaces of the pair of truncated conical rolls 02 and the accuracy of the parallelism and size between the roll axes should be high. Moreover, a large number of working steps is required. As a result, productivity is low, and it is impossible to obviate a high cost.
In addition, it has been difficult to apply the structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013 to polygonal rib structures other than the honeycomb structure.